Recently, in the medicament field, an electrochemical biosensor has been frequently used to analyze biological samples including blood. Especially, an electrochemical biosensor using an enzyme is being widely used since its application is easy, it has high measurement sensitivity, and results can be quickly obtained.
As to examples of such an electrochemical biosensor, there is a glucose measuring biosensor. The operation mechanism thereof will be described.
As to a glucose measuring biosensor, a certain electrode is formed, and then a glucose oxidase, as an analysis reagent, is immobilized onto part of the electrode to form a reaction layer. When a blood sample is introduced onto the reaction layer, glucose in the blood is oxidized by the glucose oxidase, and the glucose oxidase is reduced. An electron acceptor oxidizes the glucose oxidase and is reduced. The reduced electron acceptor loses its electrons on the electrode surface, to which predetermined voltage has been applied, and is electrochemically re-oxidized. Since glucose concentration in the blood sample is in proportion to an amount of current generated during the oxidization of the electron acceptor, glucose concentration can be measured by measuring the current amount.
By using this electrochemical biosensor, it is possible to measure uric acid and protein, in addition to glucose, in blood. Furthermore, it is possible to measure enzyme activity of GOT (Glutamate-Oxaloacetate Transaminase) or GPT (Glutamate-Pyruvate Transaminase) for DNA and liver function tests.
Herein, the biosensor is divided into an identification portion for identifying an object to be measured and a conversion portion for performing conversion into an electrical signal. For the identification portion, a biological material is used, whereby when the biological material identifies an object to be measured, a chemical or physical change occurs. The conversion portion converts the change into an electrical signal and is generally called as a biosensor electrode.
As to a method of fabricating this biosensor electrode, there is a silk printing method. A silk printing method is a printing method using platinum, carbon, or silver/silver chloride ink, which requires low equipment cost but has a problem since adjusting resistance variation to fabricate a sensor electrode requiring reproducibility is difficult.
As to another method of fabricating the biosensor electrode, there is a vacuum deposition or sputtering method using a patterned mask and precious metals. According to this method, a patterned mask is deposited on a substrate, and vacuum deposition or sputtering using precious metals is performed to form electrode patterns. However, this method is problematic since costs are expensive due to use of precious metals, and there is difficulty in recovering precious metals.
In addition, a conventional sputtering method performs sputtering by using a patterned mask. That is, since sheet-type sputtering should be performed, and long time is required to perform the sputtering, production efficiency is low.
Meanwhile, in order to fabricate a biosensor electrode, metal patterning technology, which has been conventionally used to fabricate a printed circuit board (PCB), may be applied to fabrication of an electrochemical biosensor electrode for quantifying specific substance in a biological sample such as blood.
However, in conventional PCB fabrication, an electrode is fabricated by using copper, etc. Laminating metal on the copper substrate causes a non-uniformed and lumpy surface so that the sample flows into the lower layer of the copper, and thereby generating an electrical signal disturbing a measurement value. Thus, this method was not suitable for application to fabrication of a biosensor electrode. Moreover, since copper or nickel used in the PCB is electroactive, namely unstable, at voltage generally used in an electrochemical biosensor, it was not suitable as an electrode material for an electrochemical biosensor.
An electrode material for an electrochemical biosensor should be a conductive material non-active to an enzyme. A conductive material non-active to an enzyme mostly include a semiconductor material, etc., such as carbon, platinum, palladium, gold, and indium on which a titanium oxide is doped. These materials are deposited generally by CVD (Chemical Vapor Deposition), PVD (Physical Vapor Deposition), and screen printing methods. These methods require a precise technique to achieve an accurate size and performance of an electrode. However, despite that the non-active materials other than carbon have excellent electrical characteristics, mass production thereof is difficult since they are highly expensive. Thus, in order to reduce electric resistance, depositing carbon thick by using a screen printing method is generally adopted. However, since the screen printing method using a carbon ink results in low hardness and non-uniform thickness, it has many defects such as irregularity of electric resistance, generation of carbon particles, and complicated processes.
As such, a technique of sputtering and depositing a chrome layer and a nickel layer on a substrate may be considered. However, since chrome is a metal having activity to an enzyme, in order to reduce the risk of reaction of chrome with an enzyme after LASER etching, a technique of depositing a carbon layer and sputtering a titanium layer, which exhibits a non-active characteristic to an enzyme and has high conductivity, is hereby introduced.